High dynamic range (HDR) images are images with a dynamic range that is more expansive than that of standard image formats. Typically, more image data can be encoded in HDR images than in images with lower (i.e., narrower) dynamic ranges. For example, an HDR image can allow for a greater range of dark and light values than a lower dynamic range image.
At present, most digital images are stored with a maximum of 8 bits per color channel (8 bpc). For example, in an 8 bpc digital image with red, green and blue color channels, 256 different values are possible for each of the red, green and blue values per pixel. Other values (e.g., alpha or opacity values, exposure values, etc.) also may be constrained by low dynamic range limitations. HDR images, on the other hand, provide more than 8 bpc. For example, some digital cameras have the ability to capture 12 bpc images. 16 bpc images and 32 bpc images are examples of likely possibilities in the near future. (HDR images also can be constructed from a collection of lower dynamic range images. See, e.g., Debevec et al., “Recovering High Dynamic Range Radiance Maps from Photographs,” SIGGRAPH '97 (August 1997).)
The range of possible color values in an 8 bpc image is narrower than the typical range of human visual perception. Thus, HDR images allow representation of a greater range of visual information that human beings can perceive. However, the vast majority of currently existing computer monitors are 8 bpc displays. So, if a digital image contains more than 8 bpc, a typical display is unable to take full advantage of this information. Although it is possible, using data compression techniques, to compress HDR images into lower dynamic range images, such techniques cause loss of image data. Most users, therefore, are currently unable to appreciate the value of HDR images.
Various prior techniques have addressed the problem of displaying more information for a displayed item than would ordinarily be visible on the display.
In Stone et al, “The Movable Filter as a User Interface Tool,” Proceedings of CHI94, pp. 306-312 (April 1994), the authors describe a user interface tool that combines an arbitrarily-shaped region with an operator that changes the view of objects viewed through that region. For example, a filter can be moved over a city map to reveal details of the map.
U.S. Pat. No. 4,800,379 describes selecting an area (such as a circle or square) of a “digitising table.” When a magnification option is selected, a magnified portion is displayed within the selected area.
U.S. patent application Ser. No. 10/012,001 describes an “interactive image” where each pixel location in the interactive image is assigned to one of several representative images having different characteristics. In a case where a desired interactive effect is to display a representative image having a “best” exposure or focus for a selected pixel location, image processing techniques are employed to determine which one of the several representative images represents the best exposure level or focus setting in connection with the selected pixel location. The one representative image can then be displayed.
A publicly available application known as HDRView allows a user to open an HDR image on a lower dynamic range display and shift-click on a selected pixel location in an HDR image to vary the exposure of the image in accordance with the exposure level at the selected pixel location. (A description of HDRView is available at http://athens.ict.usc.edu/FiatLux/hdrview/.)
Whatever the benefits of previous techniques, they do not have the advantages of the techniques and tools presented below.